This invention relates to electronic instruments for measuring various optical characteristics of optical, opto-electrical, and electro-optical systems, subsystems, and components, and preferably electrical characteristics, as well, and, more particularly, to instrumentation for measuring optical characteristics of optical fiber utilized in such systems, subsystems, and components. Specifically, one embodiment of the invention is directed to providing a determination of chromatic dispersion in single mode optical fiber.
Single mode optical fiber exhibits what is generally referred to as "chromatic dispersion." Chromatic dispersion is characterized by the phenomenon that optical signals having different wavelengths travel along a single mode optical fiber at different speeds.
For example, light sources, such as lasers utilized in optical communications systems, typically produce optical signals which have some inherent or modulation-induced spectral width, which results in optical signal components having different wavelengths. The effect of a chromatically dispersive single mode optical fiber on such modulation-induced optical signal components, for example, is to re-arrange the phase relationships of the modulation components, producing a distorted optical signal at the receiving end of the fiber.
Unfortunately, high-rate optical receivers in optical communications systems are particularly vulnerable to chromatic dispersion. The distinction between adjacent pulses is degraded, and the "decision," or detection, process for pulse-coded data becomes less certain.
Since experiments with spooled or deployed single mode optical fiber can be dramatically influenced by effects of chromatic dispersion, optical communications system, subsystem, and component designers must be aware of the dispersion factor at the operating, or carrier, wavelength. Accordingly, there is a particular need to determine chromatic dispersion in single mode optical fiber so that this fiber can be characterized and so that receivers in optical communications systems can be designed effectively.